//! 主从复制管理模块
//! 
//! 实现Redis集群的主从复制功能，包括：
//! - 主从关系建立和维护
//! - 复制偏移量管理
//! - 增量同步机制
//! - 复制状态监控

use crate::cluster::traits::{
    ReplicationManager as ReplicationManagerTrait, ReplicationStatus as ReplicationStatusTrait, ReplicationStats
};
use crate::cluster::{ClusterError, ClusterResult, NodeRole};
use async_trait::async_trait;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::Arc;
use std::time::{Duration, Instant};
use tokio::sync::{RwLock, mpsc};
use tokio::time::interval;
use tracing::{debug/*, error*/, info, warn};

/// 复制状态
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum ReplicationState {
    /// 未连接
    Disconnected,
    /// 连接中
    Connecting,
    /// 已连接
    Connected,
    /// 同步中
    Syncing,
    /// 在线复制
    Online,
    /// 错误状态
    Error,
}

/// 复制连接信息
#[derive(Debug, Clone)]
pub struct ReplicationConnection {
    /// 连接ID
    pub connection_id: String,
    /// 主节点ID
    pub master_id: String,
    /// 从节点ID
    pub slave_id: String,
    /// 连接状态
    pub state: ReplicationState,
    /// 建立时间
    pub connected_at: Option<Instant>,
    /// 最后心跳时间
    pub last_heartbeat: Option<Instant>,
    /// 复制偏移量
    pub replication_offset: u64,
    /// 主节点偏移量
    pub master_offset: u64,
    /// 延迟时间 (毫秒)
    pub lag_ms: u64,
    /// 错误信息
    pub error_message: Option<String>,
}

/// 复制配置
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ReplicationConfig {
    /// 心跳间隔
    pub heartbeat_interval: Duration,
    /// 复制超时时间
    pub replication_timeout: Duration,
    /// 最大复制延迟 (超过此值认为从节点不可用)
    pub max_lag_ms: u64,
    /// 全量同步阈值 (偏移量差距超过此值触发全量同步)
    pub full_sync_threshold: u64,
    /// 复制缓冲区大小
    pub replication_buffer_size: usize,
    /// 是否启用压缩
    pub enable_compression: bool,
}

impl Default for ReplicationConfig {
    fn default() -> Self {
        Self {
            heartbeat_interval: Duration::from_secs(1),
            replication_timeout: Duration::from_secs(10),
            max_lag_ms: 1000,
            full_sync_threshold: 1024 * 1024, // 1MB
            replication_buffer_size: 1024 * 1024 * 10, // 10MB
            enable_compression: false,
        }
    }
}

/// 复制事件
#[derive(Debug, Clone)]
pub enum ReplicationEvent {
    /// 主从关系建立
    MasterSlaveConnected { master_id: String, slave_id: String },
    /// 主从关系断开
    MasterSlaveDisconnected { master_id: String, slave_id: String, reason: String },
    /// 全量同步开始
    FullSyncStarted { master_id: String, slave_id: String },
    /// 全量同步完成
    FullSyncCompleted { master_id: String, slave_id: String, duration: Duration },
    /// 增量同步
    IncrementalSync { master_id: String, slave_id: String, operations: usize },
    /// 复制延迟警告
    ReplicationLagWarning { master_id: String, slave_id: String, lag_ms: u64 },
    /// 从节点下线
    SlaveOffline { master_id: String, slave_id: String },
    /// 从节点恢复
    SlaveOnline { master_id: String, slave_id: String },
}

/// 复制操作
#[derive(Debug, Clone)]
pub struct ReplicationOperation {
    /// 操作ID
    pub operation_id: u64,
    /// 操作类型
    pub operation_type: OperationType,
    /// 键名
    pub key: String,
    /// 值 (可选)
    pub value: Option<Vec<u8>>,
    /// 时间戳
    pub timestamp: Instant,
    /// 过期时间 (可选)
    pub expire_at: Option<Instant>,
}

/// 操作类型
#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
pub enum OperationType {
    Set,
    Delete,
    Expire,
    Clear,
}

/// 复制状态信息
#[derive(Debug, Clone)]
pub struct ReplicationStatus {
    pub role: String,
    pub master_id: Option<String>,
    pub slaves: Vec<String>,
    pub replication_lag: Duration,
    pub last_sync: Option<Instant>,
}

impl From<ReplicationStatus> for ReplicationStatusTrait {
    fn from(status: ReplicationStatus) -> Self {
        ReplicationStatusTrait {
            role: status.role,
            master_id: status.master_id,
            slaves: status.slaves,
            replication_lag: status.replication_lag,
            last_sync: status.last_sync,
        }
    }
}

/// 复制统计信息
#[derive(Debug, Clone, Default)]
pub struct ClusterReplicationStats {
    pub total_replications: u64,
    pub successful_replications: u64,
    pub failed_replications: u64,
    pub average_lag: Duration,
    pub data_replicated: u64,
}

impl From<ClusterReplicationStats> for ReplicationStats {
    fn from(stats: ClusterReplicationStats) -> Self {
        ReplicationStats {
            total_replications: stats.total_replications,
            successful_replications: stats.successful_replications,
            failed_replications: stats.failed_replications,
            average_lag: stats.average_lag,
            data_replicated: stats.data_replicated,
        }
    }
}

/// 主从复制管理器
pub struct ClusterReplicationManager {
    /// 本节点ID
    node_id: String,
    /// 节点角色
    node_role: NodeRole,
    /// 复制连接映射 (从节点ID -> 连接信息)
    slave_connections: Arc<RwLock<HashMap<String, ReplicationConnection>>>,
    /// 主节点连接 (如果是从节点)
    master_connection: Arc<RwLock<Option<ReplicationConnection>>>,
    /// 复制缓冲区 (存储待复制的操作)
    replication_buffer: Arc<RwLock<Vec<ReplicationOperation>>>,
    /// 事件发送器
    event_sender: mpsc::UnboundedSender<ReplicationEvent>,
    /// 事件接收器
    event_receiver: Arc<RwLock<Option<mpsc::UnboundedReceiver<ReplicationEvent>>>>,
    /// 配置
    config: ReplicationConfig,
    /// 运行状态
    is_running: Arc<RwLock<bool>>,
    /// 统计信息
    stats: Arc<RwLock<ClusterReplicationStats>>,
}

impl ClusterReplicationManager {
    /// 创建新的复制管理器
    pub fn new(
        node_id: String,
        node_role: NodeRole,
        config: Option<ReplicationConfig>,
    ) -> Self {
        let (event_sender, event_receiver) = mpsc::unbounded_channel();
        
        Self {
            node_id,
            node_role,
            slave_connections: Arc::new(RwLock::new(HashMap::new())),
            master_connection: Arc::new(RwLock::new(None)),
            replication_buffer: Arc::new(RwLock::new(Vec::new())),
            event_sender,
            event_receiver: Arc::new(RwLock::new(Some(event_receiver))),
            config: config.unwrap_or_default(),
            is_running: Arc::new(RwLock::new(false)),
            stats: Arc::new(RwLock::new(ClusterReplicationStats::default())),
        }
    }
    
    /// 获取事件接收器
    pub async fn take_event_receiver(&self) -> Option<mpsc::UnboundedReceiver<ReplicationEvent>> {
        self.event_receiver.write().await.take()
    }
    
    /// 启动心跳任务
    async fn start_heartbeat_task(&self) {
        let slave_connections = self.slave_connections.clone();
        let master_connection = self.master_connection.clone();
        let is_running = self.is_running.clone();
        let heartbeat_interval = self.config.heartbeat_interval;
        
        tokio::spawn(async move {
            let mut interval = interval(heartbeat_interval);
            
            while *is_running.read().await {
                interval.tick().await;
                
                // 更新从节点心跳
                let mut slaves = slave_connections.write().await;
                for (slave_id, connection) in slaves.iter_mut() {
                    connection.last_heartbeat = Some(Instant::now());
                    debug!("更新从节点 {} 心跳", slave_id);
                }
                
                // 如果是从节点，更新主节点心跳
                if let Some(connection) = master_connection.write().await.as_mut() {
                    connection.last_heartbeat = Some(Instant::now());
                    debug!("更新主节点 {} 心跳", connection.master_id);
                }
            }
        });
    }
    
    /// 启动主节点复制任务
    async fn start_master_replication_task(&self) {
        let replication_buffer = self.replication_buffer.clone();
        let slave_connections = self.slave_connections.clone();
        let stats = self.stats.clone();
        let is_running = self.is_running.clone();
        
        tokio::spawn(async move {
            let mut interval = interval(Duration::from_millis(100));
            
            while *is_running.read().await {
                interval.tick().await;
                
                // 检查是否有待复制的操作
                let buffer = replication_buffer.read().await;
                if !buffer.is_empty() {
                    let slaves = slave_connections.read().await;
                    
                    for (slave_id, _connection) in slaves.iter() {
                        // TODO: 实际发送复制数据到从节点
                        debug!("向从节点 {} 发送复制数据", slave_id);
                    }
                    
                    // 更新统计
                    let mut stats = stats.write().await;
                    stats.total_replications += buffer.len() as u64;
                    stats.successful_replications += buffer.len() as u64;
                }
                
                // 清空缓冲区
                drop(buffer);
                replication_buffer.write().await.clear();
            }
        });
    }
    
    /// 启动从节点复制任务
    async fn start_slave_replication_task(&self) {
        let master_connection = self.master_connection.clone();
        let stats = self.stats.clone();
        let is_running = self.is_running.clone();
        
        tokio::spawn(async move {
            let mut interval = interval(Duration::from_millis(100));
            
            while *is_running.read().await {
                interval.tick().await;
                
                if let Some(_connection) = master_connection.read().await.as_ref() {
                    // TODO: 从主节点接收复制数据
                    debug!("从主节点接收复制数据");
                    
                    // 更新统计
                    let mut stats = stats.write().await;
                    stats.total_replications += 1;
                }
            }
        });
    }
    
    /// 添加复制操作到缓冲区
    pub async fn add_replication_operation(&self, operation: ReplicationOperation) -> ClusterResult<()> {
        let mut buffer = self.replication_buffer.write().await;
        buffer.push(operation);
        
        // 限制缓冲区大小
        if buffer.len() > self.config.replication_buffer_size {
            buffer.remove(0);
        }
        
        Ok(())
    }
}

#[async_trait]
impl ReplicationManagerTrait for ClusterReplicationManager {
    async fn start(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        if *running {
            return Ok(());
        }
        *running = true;
        
        info!("启动复制管理器: 节点 {} 角色 {:?}", self.node_id, self.node_role);
        
        // 启动心跳任务
        self.start_heartbeat_task().await;
        
        // 启动复制任务
        match self.node_role {
            NodeRole::Master => {
                self.start_master_replication_task().await;
            }
            NodeRole::Slave(_) => {
                self.start_slave_replication_task().await;
            }
            _ => {
                warn!("不支持的节点角色: {:?}", self.node_role);
            }
        }
        
        Ok(())
    }
    
    async fn stop(&mut self) -> ClusterResult<()> {
        let mut running = self.is_running.write().await;
        *running = false;
        info!("复制管理器已停止: {}", self.node_id);
        Ok(())
    }
    
    async fn replicate_from(&mut self, master_id: String) -> ClusterResult<()> {
        if let NodeRole::Slave(_) = self.node_role {
            let connection = ReplicationConnection {
                connection_id: format!("repl_{}_{}", self.node_id, master_id),
                master_id: master_id.clone(),
                slave_id: self.node_id.clone(),
                state: ReplicationState::Connecting,
                connected_at: None,
                last_heartbeat: None,
                replication_offset: 0,
                master_offset: 0,
                lag_ms: 0,
                error_message: None,
            };
            
            *self.master_connection.write().await = Some(connection);
            
            info!("建立从主节点 {} 的复制关系", master_id);
            
            // 发送连接事件
            let _ = self.event_sender.send(ReplicationEvent::MasterSlaveConnected {
                master_id,
                slave_id: self.node_id.clone(),
            });
            
            Ok(())
        } else {
            Err(ClusterError::Config("只有从节点可以建立复制关系".to_string()))
        }
    }
    
    async fn add_slave(&mut self, slave_id: String) -> ClusterResult<()> {
        if let NodeRole::Master = self.node_role {
            let connection = ReplicationConnection {
                connection_id: format!("repl_{}_{}", self.node_id, slave_id),
                master_id: self.node_id.clone(),
                slave_id: slave_id.clone(),
                state: ReplicationState::Connected,
                connected_at: Some(Instant::now()),
                last_heartbeat: Some(Instant::now()),
                replication_offset: 0,
                master_offset: 0,
                lag_ms: 0,
                error_message: None,
            };
            
            self.slave_connections.write().await.insert(slave_id.clone(), connection);
            
            info!("添加从节点: {}", slave_id);
            
            // 发送连接事件
            let _ = self.event_sender.send(ReplicationEvent::MasterSlaveConnected {
                master_id: self.node_id.clone(),
                slave_id,
            });
            
            Ok(())
        } else {
            Err(ClusterError::Config("只有主节点可以添加从节点".to_string()))
        }
    }
    
    async fn remove_slave(&mut self, slave_id: &str) -> ClusterResult<()> {
        if let NodeRole::Master = self.node_role {
            if self.slave_connections.write().await.remove(slave_id).is_some() {
                info!("移除从节点: {}", slave_id);
                
                // 发送断开事件
                let _ = self.event_sender.send(ReplicationEvent::MasterSlaveDisconnected {
                    master_id: self.node_id.clone(),
                    slave_id: slave_id.to_string(),
                    reason: "主动移除".to_string(),
                });
                
                Ok(())
            } else {
                Err(ClusterError::Config(format!("从节点 {slave_id} 不存在")))
            }
        } else {
            Err(ClusterError::Config("只有主节点可以移除从节点".to_string()))
        }
    }
    
    async fn get_slave_list(&self) -> Vec<String> {
        self.slave_connections.read().await.keys().cloned().collect()
    }
    
    async fn get_replication_status(&self) -> ReplicationStatusTrait {
        let role = match self.node_role {
            NodeRole::Master => "master".to_string(),
            NodeRole::Slave(_) => "slave".to_string(),
            _ => "unknown".to_string(),
        };
        
        let master_id = self.master_connection.read().await.as_ref().map(|connection| connection.master_id.clone());
        
        let slaves = self.get_slave_list().await;
        
        // 计算平均延迟
        let connections = self.slave_connections.read().await;
        let average_lag = if connections.is_empty() {
            Duration::from_millis(0)
        } else {
            let total_lag: u64 = connections.values().map(|c| c.lag_ms).sum();
            Duration::from_millis(total_lag / connections.len() as u64)
        };
        
        let status = ReplicationStatus {
            role,
            master_id,
            slaves,
            replication_lag: average_lag,
            last_sync: Some(Instant::now()), // TODO: 记录实际的最后同步时间
        };
        
        status.into()
    }
    
    async fn get_replication_stats(&self) -> ReplicationStats {
        let stats = self.stats.read().await;
        stats.clone().into()
    }
}

